Geographic Range

Hill wallaroos are found only in western Australia in New South Wales, the Pilbara district, and Queensland. An uncommon subspecies, Macropus robustus isabellinus is limited in distribution to Barrow Island, off of Pilbara. (Arnold, et al., 1993; Ealey, 1967; Ellis, et al., 2008)

Habitat

Hill wallaroos are usually found on or in rocky hills, caves, and rock formations with large overhangs, anything that can provide shelter from the intense heat during the day. They are also commonly found in shrublands and along streams, near their main food and water sources.
A study by Taylor (1983) found that, when hill wallaroos seek shelter, larger adult males occupied much rockier areas than smaller males or females. (Ellis, et al., 2008; Taylor, 1983)

Physical Description

Hill wallaroos are bipedal marsupials with coat color varying from light gray to black. Hill wallaroo lengths can reach 100 to 140 cm. Males weigh from 28 to 42 kg and are much larger than females at 18 to 24 kg.
Compared to other wallaroos, hill wallaroos have shorter and wider torsos and shorter limbs, both presumed adaptations for their rocky terrain. They also have short but wide hind feet with powerful legs used to jump up to 4 m. The feet have roughened soles on the bottom for extra grip. (Dawson, 1995; Nowak and Wilson, 1991)

Reproduction

Hill wallaroos breed year-round and are monogamous. To attract a mate, males display their dominance to other males through frequent fighting and displaying themselves for females to see. The major way to display dominance or defending females is by initiating "boxing matches" where two males fight until one surrenders. These matches are rarely fatal. (Arnold, et al., 1993; Croft, 1982; Rose, et al., 1997)

Year-round breeding is common and the number of offspring is one per year. Breeding interval is influenced by the number of pouch young a female has, as a joey grows the female can't accommodate two joeys and must wait until one has left the pouch before another can be raised. The average gestation period is 36 days (range 30 to 38). The average time of weaning occurs around 15 to 16 months. Females wait until weaning has stopped in order to mate again. The average age of sexual maturity is 18 to 19 months for males and 22 months (range 21 to 24) for females.
When a hill wallaroo is born, the average weight is only 0.703 g. The young, or joey, stays in the mother's pouch after birth for protection. The joey is in the mother's pouch full-time until month 6, when it may tumble out of the pouch, but quickly climbs back in. Soon after, the joey becomes active and grows rapidly. By about the 37th week (231 to 270 days) of the joey's life, the mother doesn't allow the joey back into her pouch and the joey is considered independent. (Clancy and Croft, 1992; Hirst, 2005; Inns, 1982; Poole and Merchant, 1987a; Russel and Richardson, 1971)

Care for the young of Macropus robustus is mostly handled by females. As marsupials, young wallaroos spend most of their time in their mother's pouch, typically for about 9 months. After this, the young continues to have a close relationship with the mother, including resting together and grooming each other. The father provides protection against predators for the entire weaning period. After about 20 months, the young are fully independent, no longer relying on a parent for food acquisition. At this age, their relationship with the father usually weakens but their relationship with their mother stays strong. (Hirst, 2005; Russel and Richardson, 1971)

Behavior

Hill wallaroos move around by hopping on their massive hind legs. Hill wallaroos generally locomote to new feeding areas within their home range. Males sometimes interact through fighting, or "boxing" with each other. Males mostly use their powerful feet to kick-box until one contestant forfeits. Males display dominance in this way in order to maintain the social hierarchy or obtain access to females for mating. Hill wallaroos interact with each other through grooming. Grooming occurs between every individual but is more frequent between young and their mothers. Males rarely groom each other. (Arnold, et al., 1993; Croft, 1982)

Home Range

The home range of hill wallaroos depends on suitable vegetation availability. Most hill wallaroos find a large patch of vegetation and stay there, the size is typically 40 to 76 square kilometers. They have been known to travel up to 18 km outside of their home range in search of other foraging opportunities. (Arnold, et al., 1993; Croft, 1982)

Communication and Perception

The most frequent visual and tactile forms of communication observed between hill wallaroos is fighting. Most fights take the form of boxing and involve two sexually-mature males competing for females and displaying dominance. To engage in a fight, males give a head-bobbing motion where they arch their heads back and flick their neck into an erect posture. Males do this head-bobbing motion multiple times until it attracts another male's attention. The other male will then either fight or display submission.
Male hill wallaroos interact with a potential mate by sniffing her and displaying himself to her. This display includes a side-to-side sweeping motion, indicating to the female that he is ready to mate.
As an alarm to surrounding hill wallaroos, they release a sound similar to a hiss, exhaled through the nose. Then they pounds their foot on the ground and run away. (Croft, 1982)

Food Habits

Herbivorous hill wallaroos mostly graze on soft-textured grasses and shrubs. All foraging occurs mainly within the home range.
In the Pilbara district in northwest Australia, there is low rainfall, meaning poor soils and less vegetation. However, a large number of sheep (Ovis aries) pastures in this region increase the success of hill wallaroos. Additionally, their ability to conserve water makes it possible for them to persist in harsh conditions. These animals can live up to two weeks without drinking water, instead they survive on water metabolized from the plants that they eat. (Ealey, 1967; Ealey, et al., 1965; Free, et al., 1970)

Predation

Hill wallaroos are preyed on by red foxes (Vulpes vulpes), which prey on young wallaroos while they are defenseless and out of the mother's pouch. They are also preyed on by humans (Homo sapiens), which take them for pelts and meat. This hunting has been restricted by the Environmental Protection and Biodiversity Conservation Act of 1999.
Hill wallaroos avoid predators through their social habits and alarm signals. Alarm signals are powerful and loud foot stomps, followed by high-pitched hisses to warn others of danger and run away. (Banks, et al., 2000; Croft, 1982)

Ecosystem Roles

Hill wallaroos may help to disperse seeds through their grazing. They are hosts to damaging protozoan parasites, Toxoplasma gondii, which cause toxoplasmosis. Advanced stages of toxoplasmosis cause flu-like symptoms and eventually brain damage. This is a serious problem for marsupials and can cause death.
According to a study by Camps et al. (2008), there have been serious outbreaks of toxoplasmosis in most zoos in the midwestern United States. This disease mostly affects felids, but can spread to any mammal and is dangerous because the disease can spread to people.
Hill wallaroos are also impacted by cutaneous Leishmaniasis. This parasite causes skin lesions and breakdown of epidermal tissue in affected areas.
Another protozoan parasite of the wallaroo is Trichomonas vaginalis. This parasite causes trichomoniasis. This affects the urethra of the wallaroo and can cause inflammation and irritation. (Camps, et al., 2008; Dougall, et al., 2009; Dubey and Crutchley, 2008; Taylor, 1983)

Economic Importance for Humans: Positive

Hill wallaroos have historically benefited humans through the hunting and fur trade, which is now illegal due to the Environmental Protection and Biological Conservation Act of 1999. Hill wallaroos are also important models in behavior research and other research. Studies on hill wallaroos have improved our understanding of food preferences, lifespan, and reproductive phases. (Banks, et al., 2000; Camps, et al., 2008; Croft, 1982)

Economic Importance for Humans: Negative

There are no known adverse effects of Macropus robustus on humans.

Conservation Status

Hill wallaroos are listed as "least concern" by the IUCN due to their wide distribution in Australia and the fact that significant populations occur in protected areas.
Although there are no major threats, the Burrow Island subspecies of hill wallaroos are in poor health as a direct result of poor nutrition. This subspecies consists of about 18,000 individuals. (Bradshaw and King, 2008; Ellis, et al., 2008)

Contributors

Glossary

Australian

Living in Australia, New Zealand, Tasmania, New Guinea and associated islands.

acoustic

uses sound to communicate

bilateral symmetry

having body symmetry such that the animal can be divided in one plane into two mirror-image halves. Animals with bilateral symmetry have dorsal and ventral sides, as well as anterior and posterior ends. Synapomorphy of the Bilateria.

biodegradation

helps break down and decompose dead plants and/or animals

chemical

uses smells or other chemicals to communicate

diurnal

active during the day, 2. lasting for one day.

endothermic

animals that use metabolically generated heat to regulate body temperature independently of ambient temperature. Endothermy is a synapomorphy of the Mammalia, although it may have arisen in a (now extinct) synapsid ancestor; the fossil record does not distinguish these possibilities. Convergent in birds.

female parental care

parental care is carried out by females

folivore

an animal that mainly eats leaves.

food

A substance that provides both nutrients and energy to a living thing.

herbivore

An animal that eats mainly plants or parts of plants.

iteroparous

offspring are produced in more than one group (litters, clutches, etc.) and across multiple seasons (or other periods hospitable to reproduction). Iteroparous animals must, by definition, survive over multiple seasons (or periodic condition changes).

monogamous

Having one mate at a time.

motile

having the capacity to move from one place to another.

native range

the area in which the animal is naturally found, the region in which it is endemic.

saltatorial

specialized for leaping or bounding locomotion; jumps or hops.

scrub forest

scrub forests develop in areas that experience dry seasons.

sedentary

remains in the same area

sexual

reproduction that includes combining the genetic contribution of two individuals, a male and a female

social

associates with others of its species; forms social groups.

tactile

uses touch to communicate

temperate

that region of the Earth between 23.5 degrees North and 60 degrees North (between the Tropic of Cancer and the Arctic Circle) and between 23.5 degrees South and 60 degrees South (between the Tropic of Capricorn and the Antarctic Circle).

terrestrial

Living on the ground.

tropical savanna and grassland

A terrestrial biome. Savannas are grasslands with scattered individual trees that do not form a closed canopy. Extensive savannas are found in parts of subtropical and tropical Africa and South America, and in Australia.

savanna

A grassland with scattered trees or scattered clumps of trees, a type of community intermediate between grassland and forest. See also Tropical savanna and grassland biome.

temperate grassland

A terrestrial biome found in temperate latitudes (>23.5° N or S latitude). Vegetation is made up mostly of grasses, the height and species diversity of which depend largely on the amount of moisture available. Fire and grazing are important in the long-term maintenance of grasslands.

visual

uses sight to communicate

viviparous

reproduction in which fertilization and development take place within the female body and the developing embryo derives nourishment from the female.

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The Animal Diversity Web is an educational resource written largely by and for college students. ADW doesn't cover all species in the world, nor does it include all the latest scientific information about organisms we describe. Though we edit our accounts for accuracy, we cannot guarantee all information in those accounts. While ADW staff and contributors provide references to books and websites that we believe are reputable, we cannot necessarily endorse the contents of references beyond our control.

This material is based upon work supported by the
National Science Foundation
Grants DRL 0089283, DRL 0628151, DUE 0633095, DRL 0918590, and DUE 1122742. Additional support has come from the Marisla Foundation, UM College of Literature, Science, and the Arts, Museum of Zoology, and Information and Technology Services.